The guaranteed RAM in a VPS is the amount reserved for that service under normal operation. It is available to the virtual machine even when other customers on the host are busy.
Operating-system services, the control panel, databases, PHP workers, mail, caches, and application processes all use RAM. Review memory usage and swap before deciding whether an upgrade is required.
Do not treat burst or cache memory as guaranteed capacity. Check the service specification or ask support for the exact allocation for your plan.
